A wireless charging system can deliver power in a non-contact manner between a wireless power transmitting terminal and a wireless power receiving terminal. A typical wireless charging system is shown in FIG. 1. The wireless power transmitting terminal 1 comprises an input capacitance Vin, an inverter circuit 11, and a transmitting-side resonant circuit 12. The wireless power receiving terminal 2 comprises a receiving-side resonant circuit 21 and a rectifying circuit 22. The transmitting-side resonance circuit 12 and the receiving-side resonance circuit 21 are coupled to each other in a non-contact manner through an alternating magnetic field of a resonant frequency, thereby achieving wireless power transmission. The rectifying circuit 22 is used for converting an alternating current generated by the receiving-side resonant circuit 21 in response to the alternating magnetic field into a direct current output. In general, the rectifying circuit 22 may adopt a full-bridge rectifying circuit (as shown in FIG. 2) or a half-bridge rectifying circuit (as shown in FIG. 3). However, no matter which one is adopted, it can only operate in one mode, which makes the operation voltage range of the circuit relatively narrow.